SOA Patterns: New Insights or Recycled Knowledge?

Transcription

1 SOA Patterns: New Insights or Recycled Knowledge? Gregor Hohpe Software Engineer Could It Be So Easy? WSDL SOAP WS* Int MyMethod(String text) { } WebMethod Cut Copy Paste Buzzword compliant, but not a serviceoriented architecture Synchronous call stack mentality No interfaceimplementation separation 2 Web Services Best Practices 1

2 SOA on Architect's Napkin Orchestration Document Endpoint Application Conversation Transform Application Rules Architect s Dream 3 SOA on Developer's Napkin ObjectDocument Eventbased Mapping Endpoint Programming Orchestration Application Document Conversation Protocol Design Process Modeling Rules Transform Application Declarative Programming Developer s Nightmare 4 Web Services Best Practices 2

3 Serviceoriented architectures involve a variety of new programming models. We can expect to see a renaissance of design patterns that capture our experience in using them correctly. 5 Understanding Technology Syntax Basic language mechanism Artefact of crude input devices Constructs "Vocabulary": Objects, Classes, Interfaces, Inheritance Easily explained but no guidance on good design Principles Separation of Concerns, OpenClosed, etc. Help evaluate a solution Patterns Guidance 6 Web Services Best Practices 3

4 Patterns Origin C. Alexander BED ALCOVE Design problem Bedrooms make no sense. Forces First, the bed in a bedroom creates awkward spaces around it: dressing, working, watching television, sitting, are all rather foreign to the side spaces left over around a bed. Second, the bed itself seems more comfortable in a space that is adjusted to it. Solution Don't put single beds in empty rooms called bedrooms, but instead put individual bed alcoves off rooms with other nonsleeping functions, so the bed itself becomes a tiny private haven. 7 Design Patterns Mind sized chunk of information (Ward Cunningham) Humantohuman communication Expresses intent (the why vs. the how ) Observed from actual experience Not a firm rule Not copypaste code 8 Web Services Best Practices 4

5 Design Patterns in Software Development Substitute for industry standard vocabulary "Soft" around the edges Guide in the absence of strict rules Subject to hype cycle: "pattern" = "credible" 9 10 Years After GoF Why Revisit Patterns? New programming models bring new patterns. Patterns are expressed using the constructs of the underlying architectural style (e.g. OO, SOA). Good to document our knowledge when not all kinks are worked out yet. Patterns help discover higher levels of abstraction. Ultimately, some patterns can be implemented in the platform. 10 Web Services Best Practices 5

6 New Programming Models in SOA Eventbased, Asynchronous Programming Explicit state management Sequencing, timing uncertainty Declarative Programming Execution path chosen at runtime XSLT, Rules engines ObjectDocument Mapping Analogous to OR mapping: subtle, but important Process Modeling Many concurrent, longrunning instances No twophasecommit style transactions Protocol Design 11 Doodleware Only Limited Help Example Graphical process editors Graphical transformation editors We love pictures Programming in pictures tedious Scalability issues Diff, Merge mostly unsupported EAI Art Often a thin veneer over a complex (or unfamiliar) programming paradigm 12 Web Services Best Practices 6

7 New Patterns in SOA Asynchronous Messaging Patterns Conversation Patterns Orchestration Patterns Process / Workflow Patterns Endpoint Patterns Security Patterns Architectural Patterns 13 Async. Messaging Patterns Components communicate via message exchanges Simplified interaction model Compose solutions out of routing, transformation elements 65 patterns Java, C#, Axis, JMS, MSMQ, TIBCO, BizTalk 14 Web Services Best Practices 7

8 Messaging Pattern Language Application A Construction Command Document Event RequestReply Return Address Correlation Identifier Sequence Expiration Format Indicator Endpoint Routing Router ContentBased Router Filter Dynamic Filter Recipient List Splitter Aggregator Resequencer Composed Msg. Processor. ScatterGather Routing Slip Process Manager Broker Channel Router Transformation Translator Envelope Wrapper Content Enricher Content Filter Claim Check Normalizer Canonical Data Model Translator Endpoint Application B Messaging Endpoints Endpoint Messaging Gateway Messaging Mapper Transactional Client Polling Consumer EventDriven Consumer Competing Consumers Dispatcher Selective Consumer Durable Subscriber Messaging Adapter Idempotent Receiver Service Activator Messaging Channels Channel PointtoPoint Channel PublishSubcr. Channel Datatype Channel Invalid Channel Dead Letter Channel Guaranteed Messaging Channel Adapter Messaging Bridge Bus Monitoring Systems Management Control Bus Detour Wire Tap History Store Smart Proxy Test Channel Purger 15 Conversations Internal State: Processing Payment Conversation State Order Invoice Internal State: Waiting for Payment Payment Drinks Internal State: Making Drinks A process supports the desired exchange of messages through send and receive activities Each conversation corresponds to one process instance Each participant has a (potentially different) process definition 16 Web Services Best Practices 8

9 Conversation Patterns Discovery Dynamic Discovery Consult Directory Referral Establishing a Conversation Threeway Handshake Acquire Token First Rotate Tokens Address Verification Basic Conversations FireandForget RequestResponse RequestResponse with Retry Polling SubscribeNotify Quick Acknowledgment MultiParty Conversations Proxy Contingent Requests Reaching Agreement Leader Election Reaching Agreement Receiver Cancels Sender Cancels Binding Request Binding Offer Resource Management Lease Renewal Reminder Error Handling Do Nothing Retry Compensating Action 17 Process Patterns Longrunning processes Multiple instances of a process template Orchestration process across multiple services exposed as composite service WSBPEL (Business Process Execution Language) Orchestration describes the automated arrangement, coordination, and management of complex computer systems, middleware, and services. WikiPedia 18 Web Services Best Practices 9

10 Workflow Patterns (Subset) Exclusive Choice (XOR) Choose one execution path from many alternatives A B C Multiple Choice (OR) Choose several execution paths from many alternatives A B C D 19 Workflow Patterns (Subset) Synchronizing Merge Merge many execution paths. Synchronize if multiple paths are taken. A C B Wait for A and B, then execute C once Multiple Merge A B Merge many execution paths without synchronizing. C Execute C twice Discriminator Merge many execution paths without synchronizing. Execute the subsequent activity only once. A C B Execute C once as soon as A or B completes 20 Web Services Best Practices 10

11 Seems Trivial But Support by standards can be spotty. XPDL UML BPEL XLANG WSFL BPML WSCI Parallel Split Synchronization Exclusive Choice Simple Merge Multi Choice Synchronizing Merge Multi Merge / / Discriminator Deferred Choice Source: 21 TakeAway New architectural styles bring new patterns. Use pattern languages as design check list. Use pattern languages as catalog of options. Patterns often highlight subtleties that vendors like to glance over. Keep us from reinventing the wheel. Patterns harvested from actual usage. We are likely to experience a pattern renaissance. Share your knowledge. 22 Web Services Best Practices 11

12 SOA Pattern Resources: Books Enterprise Integration Patterns Gregor Hohpe, Bobby Woolf AddisonWesley, 2004 PatternOriented Software Architecture Vol.2 Schmidt et al Wiley, 2000 Integration Patterns Microsoft Patterns & Practices, 2004 PatternOriented Software Architecture Vol.4 Buschmann et al. Wiley, 2007 Essential Business Process Modeling Havey O'Reilly, 2005 SOA Patterns Arnon Rotemgaloz Manning, 2008 (?) 23 SOA Pattern Resources: Online Integration Patterns Messaging Patterns Remoting Patterns Orchestration Patterns SOA Patterns Workflow Patterns Conversation Patterns Service Interaction Patterns Data Integration Patterns Web Service Security Patterns msdn.microsoft.com/practices/topics/patterns eaipatterns.com orchestrationpatterns.com workflowpatterns.com conversationpatterns.com (WIP) serviceinteraction.com msdn.microsoft.com/practices/topics/patterns msdn.microsoft.com/practices/topics/patterns 24 Web Services Best Practices 12